DAMAGE CAUSED BY ANIMALS. 171 



cover. These schools or colonies, a characteristic of this insect, 

 often plainly discernible by the contrast of the blackish cater- 

 pillars against the brown bark of the Spruce, often hardly 

 distinguishable against either Spruce or Pine, are broken up after 

 about 4 to 6 days, when the tiny caterpillars ascend the stems to 

 commence feeding on the foliage. They attack the lower portions 

 first, and gradually work up towards the summit of the crown, 

 denuding the branches and twigs of needles as they proceed 

 upwards. Their manner of feeding is very wasteful, for only in 

 the case of the Spruce do they entirely devour the spines, whilst 

 in regard to the Pine they bite the needles through about the 

 middle, and eat only the lower portion remaining ; the foliage of 

 broad-leaved species is in the same way only partially devoured, 

 the mid-rib being gnawed through, so that the larger part of the 

 leaf falls down to the ground, which is often littered with the 

 fragments of needles and leaves when the caterpillars are very 

 numerous. 



During the process of their development, the caterpillars 

 change their skins four times, and until about half-grown they 

 are endowed with the power of spinning gossamer threads, by 

 means of which they let themselves down to the ground, or from 

 which they depend if blown or shaken down from the foliage. 



Their feeding-time lasts till about the end of June or the 

 beginning of July, when the caterpillars descend from the stems 

 in troops in order to enter the pupal state of rest under the scales 

 of the bark, or on the undergrowth, &c. 



The Black Arches moth or " Nun " (so called in Germany from 

 its plain black-and-white colouring) belongs to the most injurious 

 class of forest insects, and the devastations in Spruce and Pine 

 woods have at times been so enormous as to have totally denuded 

 very extensive areas of their foliage, and thus killed the crops. 

 Such calamitous attacks usually commence within the older crops, 

 but during high winds the young caterpillars are blown away on 

 their gossamer threads, and wafted over into pole-forests and 

 young seedling growth that may happen to be contiguous, where 

 they at once begin to feed. 1 



1 When the moths swarm in great numbers, they often migrate from one place to 

 another. Thus, it was proved beyond doubt that in the recent enormous swarms in 

 Bavaria, the moths, attracted by the brilliant lights, used to accompany the railway 

 trains for considerable distances, travelling, of course, at night. Trans. 



